Process for anodic esterification



United States Patent 7 2,829,094 PROCESS FOR ANODIC ESTERIFICATION Per Valter jhman, Bromma, Stockholm, Sweden, assignor to Dr. Ing. Mario Biazzi Soc. Am, Vevey, Switzerland, a corporation of Switzerland No Drawing Application June '7, 1954 Serial No. 435,068 7 3 Claims. (Cl. 204-80) 1 This invention relates to a process for anodic esterification in which the anolyte is a solution in an organic solvent and the catholyte is an aqeous solution and the anolyte and the catholyte are separated from one another by'a diaphragm. As examples of such esterification may be mentioned the production of. nitric acid esters of olefines with the use of calcium nitrate as salt of conductivity and source of supplying N An example of a suitable organic solvent is acetone V r It has been found that in such esterification processes it is possible to obtain a satisfactory current utilization or electrolytic efficiency only under the condition that the effective water content of-the anolyte is maintained at: a low value. Owing to its composition the anolyte has a high ohmic resistance, while the catholyte, being an aqueous solution, has a low ohmic resistance. In order to preventleakagefof current in .toogreat a degree, the diaphragm must be filled with catholyte: as far as possible which theoretically may be effected by maintaining a suitable difference'of pressure. between the anolyte'system and the catholyte system. In practice, however, it is extremely diflicult to regulate this difierence ot pressure in such a way that the water content of the anolyte does not increase in which case, the electrolytic efiiciency will rapidly decrease with increasing.v content of water in the. anolyte.

The present invention has for its object to counteract and prevent an increase of theefiective' concentration of water in the anolyte. For this purpose, according to the invention, the catolyte is brought in contact with or has added thereto a water-binding substance which substantially prevents passage of water from the catholyte through the diaphragm into the anolyte and reduces the effect of this water upon the electrolytic efliciency of the lprocess.

As an example of a suitable water-binding substance may be mentioned calcium nitrate which is suitably added in the form of anhydrous nitrate, for example in an amount of 10% by weight, based on the catholyte. Excellent results are obtained, if the addition is regulated in such a way that the content of Ca(NO in the catholyte amounts to 40% or more. Especially advantageous is an addition of the calcium nitrate in such a quantity that the -'content of water in the catholyte corresponds to or only slightly diifers from that corresponding to the hydrate with the formula Ca(NO .4H 0 which composition of the catholyte is made possible, due to the comparatively low melting point of the hydrate in question. This hydrate contains about 69% by weight of calcium nitrate. If required, the melting point may be lowered still more by addition of anhydrous or substantially anhydrous nitric acid as will be seen from the table below:

Freezing point,

Composition degrees Consequently, according tothe'invention it is possible to use at'atemperature slightly above 41 C. a catholyte consisting solely of the hydrate Ca(NO .4 H O and to lower the temperature, at which the reaction can be carried out, to a temperature under 30C., by addition or. a moderate amount of' anhydrous nitric acid, to said catholyte. From about 2't'o '15 by Weight no nitric acid: can be used in the catholyte. In reality, there would be no danger of crystallization taking. place in the dia-' phragm, even if the anolyte had a considerably lower temperature, since calcium nitrate solutions may be supercooled in a high degree. Moreover, the. diaphragm is subjected to a heating electrically which would immediately increase, if the ohmicresistance, due to crystallization, would increase.

The invention is applicablein all cases where esterification'can be carried out electrochemically. Preferred ex amples are theestificationof olefines, including pure olefinic hydrocarbons of the type ethylene, propylene, butylene etc. (exemplified by the experimental series described in Example 1 below), olefines having more than one double bond, such as methylpentadiene, butadiene et-c.. (exemplified in Example 2) and substitutedolefines containing a substituent, for example a. carboxylic. group' (exemplified in Example 3). Inthe examples below the degree of esterification obtainedis expressed. by stating the amount of nitrogen in g. per ampere/hour which is combined with the ester formed. This is a rough measure of the electrolytic efficiency of the esterification process.

Example 1 In the experiments in this series ethylene was .usedas primary material. The anolyte has in all cases the following composition: 7 7 a As anode a platinum wire gauze with a surface of 66 cm? was used. The density of current was maintained as near as possible to 3.5 amperes/dmfi. The ethylene was added.

with stirring to the.anolyte. Immediately beforethe com- *mencer'n'ent of theexperiment 20ml. catholyte was added to" the anolyte. Thisaddition wasmade substantially,v to,-

simulate the" conditions which would result from the passage of the same amount of catholyte through the diaphragm. After 30 minutes the experiments were discontinued. A-fter neutralization by addition of bicarbonate the acetone was evaporated, whereupon the oxidation product formed was extracted with ether.

The following results were obtained:

The above table shows that the loss of efficiency, due to the addition of catholyte (directly or by penetration through the diaphragm), to the anolyte, is substantially reduced when the catholyte contains at least 40% Ca(NO This is due to the water binding power of the calcium nitrate.

In the practical operation of my process the procedure outlined above is followed except for omission of the step of adding catholyte directly to the anolyte. The above tests simulate the practical process after it has been operated for a suflicient time so that 20 ml. of catholyte have passed through the diaphragm into the anolyte.

Example 2 Acetone ml 200. Ca(N .4H,O Methylpentadiene ml 10 As anode a platinum wire gauze with a surface of 156 cm. was used. The density .of current was 1.34 amperes per dm. During a period of 35 minutes 25 ml. catholyte was added to the anolyte. After 30 minutes the experiments were discontinued. After neutralization by addition of bicarbonate acetone and excess of methylpentadiene were evaporated, whereupon the oxidation product formed was extracted with ether.

The following results were obtained:

As compound to be esterified in this case crotonic acid was used. The anolyte had in all cases the following composition:

Acetone ml 100 Ca(NO,),.4H- .O g 1 Crotonic acid g 2 As anode a platinum wire gauze with a surface of 66 cm. was used. The density of current was maintained as near as possible to 3.5 arnperes/dm. Immediately before the commencement of the experiment ml. catholyte was added to the anolyte. After 30 minutes the experiments were discontinued. After neutralization by addition of bicarbonate the acetone was evaporated, whereupon the 4 mixture was acidified by addition of a small quantity of acetic acid and nitric acid. The oxidation product formed was extracted with ether and then carefully washed with water before evaporation. The following results were obtained:

g. oxldanitrogen tion content g. nitrogen Composition of the catholyte product percent per amadded to the anolyte per am- 0! the pore/hour pare/hour oxidation product What I claim is:

1. In the process of manufacturing nitric acid esters by anodic esterification, making use of a diaphragm cell in which a catholyte comprising an aqueous solution of calcium nitrate is separatedby a diaphragm from an anolyte comprising an unsaturated organic compound having at least one double bond between carbon atoms dissolved in an organic solvent therefor and an electric current is passed from an anode in theanolyte to a cathode in the catholyte; the improvement which comprises cmploying as catholyte an aqeous solution containing dissolved therein at least about 40% by weight of calcium nitrate, suflicient to reduce the decrease in electrolytic efficiency produced by the migration of aqueous catholyte through the diaphragm into the anolyte, and from about 2 to 15% of anhydrous nitric acid, suflicient to reduce the melting point ofthe catholyte below operating temperatures, whereby a high electrolytic efliciency is obtained which decreases only slowly during the electrolysis.

2. The process of claim 1 wherein the concentration of calcium nitrate in the catholyte ranges from about 40% Ca.(NO3)2;tO Ca(N03)g-4H20.

3. The process of claim 1 wherein the catholyte consists of a melt of the hydrate Ca(NO;,) .4H O containing from 2 to 15% anhydrous nitric acid.

References Cited in the file of this patent UNITED STATES PATENTS 2,130,813 Ohman Sept. 20, 1938 

1. IN THE PROCESS OF MANUFACTURING NITRIC ACID ESTERS BY ANODIC ESTERIFICATION, MAKING USE OF A DIAPHRAGM CELL IN WHICH A CATHOLYTE COMPRISING AN AQUEOUS SOLUTION OF CALCIUM NITRATE IS SEPARATED BY A DIAPHRAGM FROM AN ANOLYTE COMPRISING AN UNSATURATED ORGANIC COMPOUND HAVING AT LEAST ONE DOUBLE BEND BETWEEN CARBON ATOMS DISSOLVED IN AN ORGANIC SOLVENT THEREFOR AND AN ELECTRIC CURRENT IS PASSED FROM AN ANODE IN THE ANOLYTE TO A CATHODE IN THE CATHOLYTE: THE IMPROVEMENT WHICH COMPRISES EMPOLYING AS CATHOLYTE AN AQEOUS SOLUTION CONTAINING DISSOLVED THEREIN AT LEAST ABOUT 40% BY WEIGHT OF CALCIUM CIENCY PRODUCED BY THE MIGRATION OF AQUEOUS CATHOLYTE THROUG THE DIAPHRAGM INTO THE ANOLYTE, AND FROM ABOUT 2 TO 15% OF ANHYDROUS NITRIC ACID, SUFFICIENT TO REDUCE THE MELTING POINT OF THE CATHOLYTE BELOW OPERATING TEMPERATURES, WHEREBY A HIGH ELECTROLYTIC EFFICIENCY IS OBTAINED WHICH DECREASES ONLY SLOWLY DURING THE ELECTROLYSIS. 